1. Field of the Invention
This invention relates to heat treating, and more particularly to an apparatus and method of continuously sintering a web material with a sintering furnace wherein the web material may be a matrix of fine metallic fibers forming a porous media.
2. Prior Art Statement
The prior art has known various types of devices for sintering a metallic or ceramic object or the like. The metallic or ceramic object is typically made from a matrix of elemental metallic or ceramic components. In the sintering process, the metallic or ceramic object is placed within a heated furnace elevated to a temperature sufficient to affix the elemental components of the object one another to form a unitary structure.
The elevated temperature is sufficient to affix the elemental metallic or ceramic components together either by melting the surface of the elemental metallic or ceramic components or by surface interaction but is insufficient to melt the individual elemental metallic or ceramic components. The heating of the metallic or ceramic object during the sintering process forms the metallic or ceramic object into a unitary object without loosing the shape of the object. Accordingly, the metallic or ceramic object could be formed of the elemental metallic or ceramic components into a desired shape and then sintered to set or fix the metallic or ceramic object into the final shape as a unitary member.
One specific area of sintering metallic or ceramic objects relates to the sintering of fibrous media. In a fibrous media, a multiplicity of fine fibers are randomly oriented into a sheet forming a web of fibrous media. The web of fibrous media was compressed and was sintered to form the desired fibrous media. The fibrous media may be used for various applications such as filtration of liquids or gases or may be used as a substrate such as a catalyst carrier, a battery plate or the like.
The fibrous media was processed by stacking a plurality of sheets of fibrous media in order to economically sinter the fibrous media. The fibrous media was prepared by stacking a plurality of sheets of fibrous media with a plurality of sheets of refractory material interleaved between the sheets of the fibrous media. A weight was placed upon the top of the stack of the plurality of sheets of fibrous media and the refractory material to compress the sheets of the fibrous media into a desired thickness.
The sintering of fibrous media was accomplished by the prior art in two distinct processes. In the first sintering process, the stack of the fibrous media and the refractory material were sintered in a vacuum furnace having a desired sintering atmosphere. In the second sintering process, the stack of the fibrous media and the refractory material were sintered on a conveyor passing through a furnace having a desired sintering atmosphere.
In the first sintering process, the stack of the fibrous media and the refractory material were placed in a vacuum furnace and the furnace was evacuated. Thereafter, the sintering atmosphere was introduced into the furnace and the furnace was increased to the desired sintering temperature. After the appropriate time for sintering of the fibrous media, the furnace was allowed to cool and the sintering atmosphere was removed from the furnace and the stack of fibrous material and the refractory material was removed therefrom. The first sintering process was essentially a batch sintering process.
In the second sintering process, the stack of the fibrous media and the refractory material were placed on a continuous conveyor and passed through a heated furnace having the sintering atmosphere. The fibrous media and the refractory material were passed thorough an input zone of the sintering atmosphere prior to heating and were passed thorough an output zone of the sintering atmosphere subsequent to heating. Due to the time required for heating and cooling of the stack of the fibrous media and the refractory material, the continuous conveyor was moved slowly through the heated furnace. The second sintering process was essentially a continuous-batch sintering process.
Although the use of the continuous-batch sintering process of the furnace and continuous conveyor belt provided several advantages over the batch sintering process of the vacuum furnace, both of the batch and the continuous-batch sintering processes still had several disadvantages.
The first disadvantage of the batch and the continuous-batch sintering processes was the limitation of the physical size of the fibrous media. There was no provision in either the batch or the continuous-batch sintering processes for making fibrous media of substantially long lengths.
The second disadvantage of the batch and the continuous-batch sintering processes was the variations in the weight produced by the stack of sheets of fibrous media and the refractory material. Due to the weight of the refractory material interleaved between the sheets of fibrous media, the bottom sheet of the fibrous media was compressed by a weight greater than the weight applied to the top sheet of the fibrous media. This caused variation in the thickness of the sheets of the fibrous media.
A third disadvantage of the batch and the continuous-batch sintering processes was the time required for the stacking of sheets of fibrous media with the interleaved refractory material therebetween. Typically, this process was done by a hand operation thus adding to the overall cost of the fibrous material.
A fourth disadvantage of the batch and the continuous-batch sintering processes was the cost associated with the sintering process. The sintering process is expensive and representing a significant portion of the cost of sintered fibrous media. If the cost of sintered fibrous media could be reduced, the lower cost of the sintered fibrous media opens the opportunity for new uses of the sintered fibrous media. The superior performance of sintered fibrous media over other types of material would provide a substantial economic advantage if the cost of sintered fibrous media could be reduced by technological processes.
The use of continuous processing furnaces have been known to the prior art for various heating tasks. Continuous processing furnaces have been used for the annealing, drying, coating processes and the like.
U.S. Pat. No. 1,856,444 to Sutton discloses a combination of a wire annealing furnace including means for moving the work to be annealed relatively fast through the furnace. An endless feed wire extends through the furnace with a part of the feed wire being located inside the furnace and with a part of the feed wire being located outside of the furnace. The feed wire is adapted to remain stationary while the work wire is moving through the furnace during the annealing operation. The feed wire is attached to the work wire for threading the work wire through the furnace.
U.S. Pat. No. 2,319,300 to Cook discloses an apparatus for heat treating strip metal comprising a furnace chamber and a pair of rotatable pulleys within the furnace chamber. An endless imperforate metallic belt is mounted entirely within the furnace chamber. A second pair of rotatable pulleys within the furnace chamber mounts a second endless imperforate metallic belt located entirely within the furnace chamber. The pairs of pulleys are positioned and spaced that portions of the belts are mounted in opposed parallel relation to each other and are spaced apart sufficiently to receive a strip of metal therebetween with the opposite faces of the strip in contact with the opposed parallel portions of the endless belts.
U.S. Pat. No. 2,838,420 to Valente discloses a method of producing an impregnated web in which the impregnant is substantially uniformly distributed throughout the thickness of the web. The method comprises introducing into a porous web a volatile liquid vehicle in such quantity and containing an impregnant in low enough concentration that the vehicle is present in the web as a continuous liquid body throughout the thickness of the web and the impregnant is mobile within the web in response to forces established by drying the web. A gaseous drying medium is passed through the web in alternately opposite directions before and until the continuous liquid body is interrupted but the web is still wet with the vehicle and contains a substantial quantity thereof capable of being evaporated by a conventional drying process to immobilize the impregnant in the web. The web is further dried sufficiently to permit handling.
U.S. Pat. No. 2,999,675 to Erhardt, Jr., et al. teaches an apparatus for heat-treating a continuous length of work comprising a movable heater having a pair of opposed panels of a size at least equal to the width of the work with each panel carrying a plurality of heating elements facing the sides of an interposed length of work. The heater is mounted for movement from a first position with the panels on opposite sides of the work to a second position beyond one edge of the work. Fuel is supplied to the elements in either position of the heater. The heater assembly is retracted laterally from the first position to the second position upon the stopping of the work.
U.S. Pat. No. 3,476,840 to Glassford discloses synthetic resin shapes molded from a continuous sheet of thermoplastic synthetic resin material by feeding a continuous sheet of the resin into a furnace in which the sheet is heat softened into a pliable, moldable state and is incidentally caused to sag. The sagging portion of the sheet is supported by means of a narrow metal band traveling beneath the sheet in the same direction and at the same rate as the sheet. The metal band is maintained at a predetermined temperature whereby the physical contact between the softened sheet and the supporting band does not mar or discolor the surface of the sheet. The softened sheet is fed directly into a molding or forming means and cooled to form molded articles.
U.S. Pat. No. 3,810,735 to Moser teaches a fixing system for fixing fusible material such as electroscopic particles upon support material. The system includes at least one fuser member in the form of an endless belt in pressure contact with another fuser member and between which the support material is transported. The fusing belt member is provided with a heat barrier blanket and is coated with a release agent that will prevent offset of the particles being fused.
U.S. Pat. No. 4,288,212 to Vertegaal discloses a method and apparatus for fixing the binding agent of a dye-stuff to a printed web of material by means of heat applied to the web within a treatment or polymerization chamber. The treatment time of the web is increased by effecting a loop formation of the web upon a slowly moving belt traveling within the treatment chamber. The web is first introduced into the chamber and is heated. Thereafter, the loop formation takes place. Upon leaving the treatment chamber, the web is passed over a stationary, curved shape heated plate, which smooths the web.
Although the aforementioned patents have solved many of the various needs through the use of a continuous processing furnace, none of the aforementioned patents is suitable for continuously sintering a web material with a sintering furnace.
Accordingly, it is an object of the present invention to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace which overcomes the aforementioned problems of the prior art and provides a significant advancement in the manufacture of sintered media.
Another object of this invention is to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace which may accommodate web material of extended lengths.
Another object of this invention is to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace wherein the apparatus may be used with delicate web material such as a matrix of fine metallic fibers.
Another object of this invention is to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace wherein a single sheet of fibrous material may be sintered with meaningful, economical results.
Another object of this invention is to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace which is able to be automated thereby eliminating the need to hand assemble the stack of sheets of fibrous media.
Another object of this invention is to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace which is capable of producing fibrous media with more consistent characteristics then provided by the sintering furnaces of the prior art.
Another object of this invention is to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace which sintered media in a faster and more than efficient manner as well as provides a more uniform sintered material.
Another object of this invention is to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace which provides a uniform weight to the sintered material during the sintering process.
Another object of this invention is to provide an improved apparatus and method of continuously sintering a web material with a sintering furnace which provides sintered fibrous material at reduced cost.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention, the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.